Do I need to clean a harmonica? If so, how often?

Yes, it is definitely a good idea to clean your harmonica, preferably every day. It's easy though, just run it under lukewarm water and let it dry. Brushing your teeth before you play will keep the harmonica nice and fresh too.

What type of microphone should I use when playing a harmonica live?

Microphone choice is always highly subjective but the famous harmonica mic is a Shure 520DX Bullet mic. It is specially shaped so that harmonica players can easily hold it whilst playing and it gives that great raunchy Blues sound.

What is a fixed key harmonica?

A fixed key harmonica is a harmonica that only plays notes in a certain key. For example, a Hohner Marine Band harmonica in the key of 'A' will only play notes in the key of A. So, providing you select the appropriate key, you will never play a wrong note!